Chemical element · reference page

12Mg

Magnesium

Magnesium is element 12 (Mg), located in period 3, group 2 and the s block. At room temperature its reference phase is solid. Its electron configuration is [Ne] 3s2.

Atomic number12

Standard atomic weight[24.304, 24.307]

Group2

Period3

Blocks

Electron configuration[Ne] 3s2

Electronic structure

What controls its chemistry

The outer configuration ends in s². Removing two valence electrons produces a +2 ion, which is the characteristic ionic state of the alkaline-earth metals.

Compared with group 1 metals, the two-electron outer shell changes ionisation energies, bonding and reactivity. Their compounds commonly occur as oxides, carbonates, sulfates or halides rather than as free metals in nature.

Chemical forms

Compounds, ions and materials

The +2 oxidation state dominates. Oxides, hydroxides, halides, carbonates and sulfates are common families of magnesium compounds, although their solubility and thermal stability vary systematically down group 2.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 1.738 g/cm³. The melting point is 923 K (649.9 °C). The boiling point is 1 363 K (1 090 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where magnesium is found and used

In practice, magnesium is encountered in alloys, fireworks and biology.

In practice

Examples of real uses

Alloys

Magnesium is added to metals to change strength, corrosion resistance, melting behaviour or high-temperature performance.

Fireworks

Magnesium compounds can produce characteristic colours, sparks or energetic effects when heated in pyrotechnic mixtures.

Biology

Magnesium ions or compounds participate in biological structures, enzymes, signalling or metabolism.

Periodic position

What its neighbours tell us

Magnesium is in period 3 and group 2. In the neighbourhood shown here, sodium is immediately to its left in the same period; beryllium is above it and calcium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationalkaline earth metal

Phase at room temperatureSolid

Electron shells2 · 8 · 2

Density1.738 g/cm³

Melting point923 K (649.9 °C)

Boiling point1 363 K (1 090 °C)

Pauling electronegativity1.31

First ionisation energy737.7 kJ/mol

Electron affinity—

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of magnesium is associated with Joseph Black. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is given as the interval [24.304, 24.307]. Natural samples can differ slightly in isotope proportions, so a single universal decimal value would hide real variation between materials.

Magnesium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with magnesium depend on chemical form, dose and route of exposure. Pure magnesium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.